OPM2 cells were crosslinked, lysed and sonicated. For ChIP with reference exogenous genome, spike-in chromatin (Active Motif, 53083) was then added. The protein-bound DNA fragments were then immunoprecipitated with specific antibodies. After reverse-crosslinking, DNA was purified. Libraries were prepared using ThruPLEX DNA-seq Kit (Rubicon Genomics) according to the manufacturer's instructions. Libraries were prepared using ThruPLEX DNA-seq Kit (Rubicon Genomics) according to the manufacturer's instructions.